added support for PLS path rendering

BUG=skia:3555
GOLD_TRYBOT_URL= https://gold.skia.org/search2?unt=true&query=source_type%3Dgm&master=false&issue=1541903002

Committed: https://skia.googlesource.com/skia/+/7df3f5e127f8016d17b637cc48a6a4718f1a6822

Review URL: https://codereview.chromium.org/1541903002
diff --git a/src/gpu/glsl/GrGLSLFragmentShaderBuilder.h b/src/gpu/glsl/GrGLSLFragmentShaderBuilder.h
index 820cf17..e998458 100644
--- a/src/gpu/glsl/GrGLSLFragmentShaderBuilder.h
+++ b/src/gpu/glsl/GrGLSLFragmentShaderBuilder.h
@@ -33,7 +33,8 @@
      */
     enum GLSLFeature {
         kStandardDerivatives_GLSLFeature = 0,
-        kLastGLSLFeature = kStandardDerivatives_GLSLFeature
+        kPixelLocalStorage_GLSLFeature = 1,
+        kLastGLSLFeature = kPixelLocalStorage_GLSLFeature
     };
 
     /**
@@ -66,6 +67,8 @@
     bool hasCustomColorOutput() const { return fHasCustomColorOutput; }
     bool hasSecondaryOutput() const { return fHasSecondaryOutput; }
 
+    void declAppendf(const char* fmt, ...);
+
 protected:
     bool fHasCustomColorOutput;
     bool fHasSecondaryOutput;